Why Light Switches May Not Be Working

How to Fix Wiring Problems with Light Switches: The Most Common Problems with Wiring Light Switches and How to Fix Them. Wiring More Than One Light Switch in the Same Switch Box

Guide to Wiring Multiple Light Switches

Electrical Question: I have a 3 way light switch that is not working.

One switch controls the hallway light the other controls the outside light and one is not used.

I went to turn on the outside light and it would not work.

I checked the circuit breaker and it was good.

When I came home the other day and flipped the switch and the light was working.

Tonight I tried the light switch again and no light.

I am not sure what could be happening except maybe a short somewhere.

This electrical question came from: Mike, a Homeowner from meridian , Idaho.
See more about Home Wiring for Idaho

Additional Comments: Great site.

Dave’s Reply:
Thanks for your electrical question Mike.

How to Fix Wiring Problems with Light Switches

Application: Wiring Light Switches.
Skill Level: Intermediate to Advanced, best installed by a licensed electrical contractor.
Tools Required: Basic Electricians Pouch Hand Tools and a Voltage Tester.
Estimated Time: Depends on personal level experience, ability to work with tools and the access to the switch box for wiring for the switches.
Precaution: Identify the circuit, turned it OFF and Tag It with a Note before working with the light switch wiring.
Notice: Modifying existing wiring or installing additional electrical wiring should be done according to local and national electrical codes with a permit and be inspected.

The Most Common Problems with Wiring Light Switches and How to Fix Them

When wiring more than one light switch in the same switch box the power source(s) will need to be identified and the circuit wiring must be understood in order to make the correct wiring connections for all of the light switches within the same switch box. The following guide will help you identify the circuit wiring.

Wiring More Than One Light Switch in the Same Switch Box

Identifying the Circuit Power

Power In: The incoming power source(s) must be identified.

Power Out: The outgoing power feeds must be identified

The circuits of the power source must not become overloaded.

Keep in mind that the circuit may supply power other devices such as receptacle outlets.

Keep the Circuit Wiring Isolated

If it is found that there are more than one circuit then be sure to keep the individual circuits isolated.

White neutral wires should be isolated as well unless the neutral is being shared within a multi-wire set.

Three Way Switch Wiring

Key Factor of Typical Light Switch Wiring:

Light switches switch the power side of the circuit, not the neutral.

Remember that white wires may not always be a neutral wire, especially if you see a white wire that is connected to a light switch.

Use a voltage tester to verify the circuit wiring configurations.

When a white wire is attached to a 3-way switch a tester may not read the power because of the position of the other 3-way switch.

Short Circuit in Electrical Wiring

If you have several light switches or light fixtures that are not working then there may be a short in the electrical wring, or most likely a loose connection has developed.

Typically the location of the electrical short will need to located after identifying all of the affected devices that are on the circuits that are not functioning.

A series of inspections of all the devices of the same circuit will need to be performed until the cause is located, and then the necessary repairs will be required.

When working on home electrical wiring using voltage testers can play an important part in electrical safety. Electrical testers enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.Types of Electrical Testers

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Hi Joe,
Here are some possibilities why a light fixture is not working after a replacement switch has been installed:
No circuit power to the switch – Make sure the circuit is on.
A faulty light switch – The switch should be tested..
The wrong replacement switch has been installed – Make sure the replacement switch is correct.
The switch is not wired correctly – Be sure the wiring configuration is as it was before replacing the switch.
The light bulb(s) are bad and need to be replaced.
I hope this helps.
Dave

I’m installing a new light switch. There were two black wires and one green wire connected to the old switch. I connected the ground wire to the new switch and the two black wires to the side connecters but the light will not come on.

ELECTRICAL SAFETY

Electrical Wiring and Electrical Repairs

Unless otherwise posted, please refer to the following Guidelines for Electrical Projects:
Skill Level:
Intermediate to Advanced - Electrical Repairs and Circuit Wiring is Best Performed by a Certified Electrician or Licensed Electrical Contractor.
Electrical Tools Required:
Basic Electricians Pouch of Hand Tools, a Voltage Tester and a Multi Meter.
Estimated Time:
Depends on personal level experience, ability to work with tools, work with electrical wiring, and the available access to the project area.
Precaution:
Identify the project circuit, turn it OFF and Tag it with a Note before working with the wiring.
Important:
Modifying existing electrical circuits or installing additional electrical wiring should be done according to local and National Electrical Codes, with a permit and be inspected.

Part P - Electrical Safety is registered Crown Copyright of the UK Government Planning Department for Communities
CE and Canadian Electrical Code CSA C22.1 are registered trade marks of the Canadian Standards Association (CSA)
NEC and National Electrical Code are registered trade marks of the National Fire Protection Association (NFPA)